Technical Field
The present disclosure concerns a ring generator of a wind power installation. In addition the present disclosure concerns a method of controlling a wind power installation and further concerns a wind power installation.
Description of the Related Art
A wind power installation converts mechanical work taken from the wind into electric energy by means of an electric generator. In that respect a ring generator is a slowly rotating generator which manages without a transmission between the rotor of the generator and the mechanical rotor assembly which has rotor blades. For that purpose the ring generator has a multiplicity of poles. The number of poles can be of the order of magnitude of 20 up to 84 poles and even more. In that respect the ring generator is of a comparatively large diameter in comparison with its axial extent. For example the ring generator of a modern wind power installation of 7 or more megawatts nominal power is of a diameter at the air gap of about 10 m whereas the extent of the air gap in the axial direction is in the region of 1 m. In that respect, as is known, the air gap is the intermediate space between the stator and the rotor of an electric generator. The rotor and/or the stator substantially assume the shape of a ring, which is thought to be the reason for identifying it as a ring generator.
Because of the slow speed of rotation of a rotor of a ring generator of a wind power installation, which can be in the range of about 5 to 50 and in particular 10 to 30 revolutions per minute as the nominal rotary speed, self-cooling by a propeller which is mechanically fixedly connected to the rotor is out of the question or is at least of little efficiency. In comparison therewith attention is directed to other generators which are used in wind power installations together with a step-up transmission and involve nominal rotary speeds in the region of some thousand revolutions per minute. Solutions in respect of such generators cannot be applied to slowly rotating ring generators.
DE 196 36 591 A1 discloses a generator for transmission-less wind converters in the form of an external rotor. There the entire magnetically operative part of the generator is arranged outside a wind power installation pod. An external rotor is especially proposed for reasons of cooling, wherein the rotor is arranged outside the stator, in a radial view. Carrier arms extend from the mounting arranged within the stator, to the externally arranged rotor. Those carrier arms of the rotor are at the same time in the form of vanes to convey cooling air into cooling passages of the stator. Such a structure however is extremely complicated and expensive.
DE 10 2004 046 700 B4, for a wind power installation with a ring generator in the form of an internal rotor, proposes urging air into the pod and through the ring generator air gap by a fan in the pod casing in order thereby to cool the ring generator.
As further general state of the art attention is to be directed to the following documents: DE 102 46 690 A1; DE 600 21 492 T2; DE 196 08 286 B4; DE 600 29 977 T2; EP 1 837 519 A2 and DE 102 ×947 A1.
To increase the cooling of a ring generator the stator and in particular the stator ring can be prepared for water cooling, in particular for guiding a flow of water. A disadvantage in that respect however is that the use of water cooling basically entails the risk of corrosion, in particular for a metallic article such as the stator ring.